共用题干 Older Volcanic EruptionsVolcanoes were more destructive in ancient hist...

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问题共用题干 Older Volcanic Eruptions
Volcanoes were more destructive in ancient history,not because they were bigger,but because the carbon dioxide they released wiped out life with greater ease.
Paul Wignall from the University of Leeds was investigating the link between volcanic eruptions and mass extinctions.Not all volcanic eruptions killed off large numbers of animals,but all the mass extinctions over the past 300 million years coincided with huge formations of volcanic rock.To his surprise,the older the massive volcanic eruptions were,the more damage they seemed to do.He calculated the"killing efficiency" for these volcanoes by comparing the proportion of life they killed off with the volume of lava（熔岩）that they produced.He found that size for size,older eruptions were at least 10 times as effective at wiping out life as their more recent rivals.
The Permian（二叠纪）extinction,for example,which happened 250 million years ago,is marked by floods of volcanic rock in Siberia that cover an area roughly the size of western Europe.Those volcanoes are thought to have pumped out about 10 gigatonnes of carbon as carbon dioxide.The global warming that followed wiped out 80 percent of all marine genera（种类）at the time,and it took 5 million years for the planet to recover.Yet 60 million years ago,there was another huge amount of volcanic activity and global warming but no mass extinction.Some animals did disappear but things returned to normal within ten thousand of years."The most recent ones hardly
have an effect at all,"Wignall says.He ignored the extinction which wiped out the dinosaurs 65 million years ago,because many scientists believe it was primarily caused by the impact of an asteroid（小行星）.He thinks that older volcanoes had more killing power because more recent life forms were better adapted to dealing with increased levels of CO₂．
Vincent Courtill.ot,director of the Paris Geophysical Institute in France,says that Wignall's idea is provocative.But he says it is incredibly hard to do these sorts of calculations.He points out that the killing power of volcanic eruptions depends on how long they lasted.And it is impossible to tell whether the huge blasts lasted for tliousands or millions of years.He also adds that it is difficult to estimate how much lava prehistoric volcanoes produced,and that lava volume may not necessarily correspond to carbon dioxide emissions。

选项 How did Wignall calculate the killing power of those older volcanic eruptions? A:By estimating how long they lasted. B:By counting the dinosaurs they killed. C:By studying the chemical composition of lava. D:By comparing the proportion of life wiped out with the volume of lava produced.

答案 D

解析由文章第一段可知，远古火山喷发更具破坏力，不是因为它们规模更大，而是因为它们释放出的二氧化碳更容易毁灭生命。故选A。
由文章第二段第四句话“He calculated the ‘ killing efficiency ' for those… they are produced.”可知，Wignall通过比较火山释放的熔岩的体积与杀死生命的比例计算这些火山的杀伤力。故选D0
由文章第三段倒数第二句话“He ignored the extinction which wiped out the dinosaurs 65 million years ago …”可知，恐龙是在6500万年前灭绝的。故选D。
由文章第三段倒数第二句话“… because many scientists believe it was primarily caused by the impact of an asteroid.”可知，Wignall没有提6500万年前恐龙的灭绝是否跟火山爆发有关是因为许多科学家认为恐龙的灭绝是由一颗小行星的影响造成的。由此可推断出关于恐龙灭绝的原因在科学家之间是有分歧的。故选D。
文章第一段直接点明了文章的主要论点。" Volcanoes were more destructive in ancient history..."（古代火山喷发更具破坏力）。故选B。

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共用题干 Older Volcanic EruptionsVolcanoes were more destructive in ancient hist...

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